Re: Debian 11 installer crashed and reboot

[Chuck Zmudzinski <brchuckz@netscape.net>]

On 8/21/2021 7:06 PM, Chuck Zmudzinski wrote:
> On 8/21/2021 5:52 AM, Thomas Schmitt wrote:
> > Hi,
> >
> > there might be an easier way (still depending on whether such simple
> > file replacements are tolerated by the booting system):
> >
> >    # Choose the desired new files
> > new_kernel=...path.to.desired.new.kernel.in.some.mounted.filesystem...
> > new_initrd=...path.to.desired.new.initrd.in.some.mounted.filesystem...
> >
> >    # Choose the files in the ISO to be replaced by the new files.
> >    # The ISO needs not to be mounted. (Better it should not be mounted.)
> >    # Naively, i assume that it's about these two:
> >    old_kernel=/install.amd/xen/vmlinuz
> >    old_initrd=/install.amd/xen/initrd.gz
> >
> >    # Copy netinst ISO to playground ISO
> >    cp debian-11.0.0-amd64-netinst.iso test.iso
> >
> >    # Use xorriso multi-session to override the undesired files
> >    xorriso -dev test.iso \
> >            -boot_image any keep \
> >            -map "$new_kernel" "$old_kernel" \
> >            -map "$new_initrd" "$old_initrd"
> >
> > This will result in a quite short run of xorriso, which will report
> > something like
> >
> >    ISO image produced: 8108 sectors
> >    Written to medium : 8288 sectors at LBA 193024
> >    Writing to 'test.iso' completed successfully.
> >
> > (The numbers 8108 and 8288 are result of the sizes of the two dummy 
> > files
> > which i used as $new_kernel #and new_initrd. Yours will be substantially
> > larger due to the typical size of an initrd.)
> >
> > Inspection of the boot equipment of test.iso shows no differences,
> > except the new storage position of the El Torito boot catalog and the
> > enlarged ISO image size.
> >
> > When mounted by Linux, the paths
> >    /mnt/iso/install.amd/xen/vmlinuz
> >    /mnt/iso/install.amd/xen/initrd.gz
> > lead to the content of $new_kernel and $new_initrd.
> >
> > Then it depends on the inner doings of boot loader and starting system,
> > whether this perky change is tolerated.
> >
> >
> > Have a nice day :)
> >
> > Thomas
>
> Hi Thomas,
>
> Thank you for these tips. I will use them to try to get a bullseye
> Debian installer ISO working in a Xen HVM DomU next week
> when I have some spare time and post the results here.
>
> All the best,
>
> Chuck

This approach (using xorriso with -dev, -boot_image, and -map options)
works to change the kernel and ramdisk on the ISO, and the new
ISO does boot into a Xen HVM without crashing and rebooting, but I
still have not succeeded in getiing the ramdisk configured correctly to
boot the Debian installer. Using the ramdisk of a full install on the
ISO causes init to drop to an initramfs shell because that ramdisk
is not configured to start the Debian installer but instead expects a
root filesystem to be passed to it on the linux kernel command line.

I expect it is possible to create a ramdisk that will successfully boot
the Debian installer in a Xen HVM. I think some components from
the ramdisk of a full install are needed to prevent the crash and
reboot, and it is a matter of identifying what components from
the ramdisk of a full install are needed. I would suspect some
kernel module that a Xen HVM needs is missing from the ramdisks
on the installation ISO.

I will continue to work on it this week in my spare time.

Cheers,

Chuck